/*
 * Copyright (c) 1988 Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/*
 * Code to handle displaying line numbers.
 *
 * Finding the line number of a given file position is rather tricky.
 * We don't want to just start at the beginning of the file and
 * count newlines, because that is slow for large files (and also
 * wouldn't work if we couldn't get to the start of the file; e.g.
 * if input is a long pipe).
 *
 * So we use the function add_lnum to cache line numbers.
 * We try to be very clever and keep only the more interesting
 * line numbers when we run out of space in our table.  A line
 * number is more interesting than another when it is far from
 * other line numbers.   For example, we'd rather keep lines
 * 100,200,300 than 100,101,300.  200 is more interesting than
 * 101 because 101 can be derived very cheaply from 100, while
 * 200 is more expensive to derive from 100.
 *
 * The function currline() returns the line number of a given
 * position in the file.  As a side effect, it calls add_lnum
 * to cache the line number.  Therefore currline is occasionally
 * called to make sure we cache line numbers often enough.
 */

#include <sys/types.h>
#include <stdio.h>
#include <less.h>

/*
 * Structure to keep track of a line number and the associated file position.
 * A doubly-linked circular list of line numbers is kept ordered by line number.
 */
struct linenum
{
        struct linenum *next;           /* Link to next in the list */
        struct linenum *prev;           /* Line to previous in the list */
        off_t pos;                      /* File position */
        off_t gap;                      /* Gap between prev and next */
        int line;                       /* Line number */
};
/*
 * "gap" needs some explanation: the gap of any particular line number
 * is the distance between the previous one and the next one in the list.
 * ("Distance" means difference in file position.)  In other words, the
 * gap of a line number is the gap which would be introduced if this
 * line number were deleted.  It is used to decide which one to replace
 * when we have a new one to insert and the table is full.
 */

#define NPOOL   50                      /* Size of line number pool */

#define LONGTIME        (2)             /* In seconds */

int lnloop = 0;                         /* Are we in the line num loop? */

static struct linenum anchor;           /* Anchor of the list */
static struct linenum *freelist;        /* Anchor of the unused entries */
static struct linenum pool[NPOOL];      /* The pool itself */
static struct linenum *spare;           /* We always keep one spare entry */

extern int linenums;
extern int sigs;

/*
 * Initialize the line number structures.
 */
clr_linenum()
{
        register struct linenum *p;

        /*
         * Put all the entries on the free list.
         * Leave one for the "spare".
         */
        for (p = pool;  p < &pool[NPOOL-2];  p++)
                p->next = p+1;
        pool[NPOOL-2].next = NULL;
        freelist = pool;

        spare = &pool[NPOOL-1];

        /*
         * Initialize the anchor.
         */
        anchor.next = anchor.prev = &anchor;
        anchor.gap = 0;
        anchor.pos = (off_t)0;
        anchor.line = 1;
}

/*
 * Calculate the gap for an entry.
 */
static
calcgap(p)
        register struct linenum *p;
{
        /*
         * Don't bother to compute a gap for the anchor.
         * Also don't compute a gap for the last one in the list.
         * The gap for that last one should be considered infinite,
         * but we never look at it anyway.
         */
        if (p == &anchor || p->next == &anchor)
                return;
        p->gap = p->next->pos - p->prev->pos;
}

/*
 * Add a new line number to the cache.
 * The specified position (pos) should be the file position of the
 * FIRST character in the specified line.
 */
add_lnum(line, pos)
        int line;
        off_t pos;
{
        register struct linenum *p;
        register struct linenum *new;
        register struct linenum *nextp;
        register struct linenum *prevp;
        register off_t mingap;

        /*
         * Find the proper place in the list for the new one.
         * The entries are sorted by position.
         */
        for (p = anchor.next;  p != &anchor && p->pos < pos;  p = p->next)
                if (p->line == line)
                        /* We already have this one. */
                        return;
        nextp = p;
        prevp = p->prev;

        if (freelist != NULL)
        {
                /*
                 * We still have free (unused) entries.
                 * Use one of them.
                 */
                new = freelist;
                freelist = freelist->next;
        } else
        {
                /*
                 * No free entries.
                 * Use the "spare" entry.
                 */
                new = spare;
                spare = NULL;
        }

        /*
         * Fill in the fields of the new entry,
         * and insert it into the proper place in the list.
         */
        new->next = nextp;
        new->prev = prevp;
        new->pos = pos;
        new->line = line;

        nextp->prev = new;
        prevp->next = new;

        /*
         * Recalculate gaps for the new entry and the neighboring entries.
         */
        calcgap(new);
        calcgap(nextp);
        calcgap(prevp);

        if (spare == NULL)
        {
                /*
                 * We have used the spare entry.
                 * Scan the list to find the one with the smallest
                 * gap, take it out and make it the spare.
                 * We should never remove the last one, so stop when
                 * we get to p->next == &anchor.  This also avoids
                 * looking at the gap of the last one, which is
                 * not computed by calcgap.
                 */
                mingap = anchor.next->gap;
                for (p = anchor.next;  p->next != &anchor;  p = p->next)
                {
                        if (p->gap <= mingap)
                        {
                                spare = p;
                                mingap = p->gap;
                        }
                }
                spare->next->prev = spare->prev;
                spare->prev->next = spare->next;
        }
}

/*
 * If we get stuck in a long loop trying to figure out the
 * line number, print a message to tell the user what we're doing.
 */
static
longloopmessage()
{
        ierror("Calculating line numbers");
        /*
         * Set the lnloop flag here, so if the user interrupts while
         * we are calculating line numbers, the signal handler will 
         * turn off line numbers (linenums=0).
         */
        lnloop = 1;
}

/*
 * Find the line number associated with a given position.
 * Return 0 if we can't figure it out.
 */
find_linenum(pos)
        off_t pos;
{
        register struct linenum *p;
        register int lno;
        register int loopcount;
        off_t cpos, back_raw_line(), forw_raw_line();
        time_t startime, time();

        if (!linenums)
                /*
                 * We're not using line numbers.
                 */
                return (0);
        if (pos == NULL_POSITION)
                /*
                 * Caller doesn't know what he's talking about.
                 */
                return (0);
        if (pos == (off_t)0)
                /*
                 * Beginning of file is always line number 1.
                 */
                return (1);

        /*
         * Find the entry nearest to the position we want.
         */
        for (p = anchor.next;  p != &anchor && p->pos < pos;  p = p->next)
                continue;
        if (p->pos == pos)
                /* Found it exactly. */
                return (p->line);

        /*
         * This is the (possibly) time-consuming part.
         * We start at the line we just found and start
         * reading the file forward or backward till we
         * get to the place we want.
         *
         * First decide whether we should go forward from the 
         * previous one or backwards from the next one.
         * The decision is based on which way involves 
         * traversing fewer bytes in the file.
         */
        flush();
        (void)time(&startime);
        if (p == &anchor || pos - p->prev->pos < p->pos - pos)
        {
                /*
                 * Go forward.
                 */
                p = p->prev;
                if (ch_seek(p->pos))
                        return (0);
                loopcount = 0;
                for (lno = p->line, cpos = p->pos;  cpos < pos;  lno++)
                {
                        /*
                         * Allow a signal to abort this loop.
                         */
                        cpos = forw_raw_line(cpos);
                        if (sigs || cpos == NULL_POSITION)
                                return (0);
                        if (loopcount >= 0 && ++loopcount > 100) {
                                loopcount = 0;
                                if (time((time_t *)NULL)
                                    >= startime + LONGTIME) {
                                        longloopmessage();
                                        loopcount = -1;
                                }
                        }
                }
                lnloop = 0;
                /*
                 * If the given position is not at the start of a line,
                 * make sure we return the correct line number.
                 */
                if (cpos > pos)
                        lno--;
        } else
        {
                /*
                 * Go backward.
                 */
                if (ch_seek(p->pos))
                        return (0);
                loopcount = 0;
                for (lno = p->line, cpos = p->pos;  cpos > pos;  lno--)
                {
                        /*
                         * Allow a signal to abort this loop.
                         */
                        cpos = back_raw_line(cpos);
                        if (sigs || cpos == NULL_POSITION)
                                return (0);
                        if (loopcount >= 0 && ++loopcount > 100) {
                                loopcount = 0;
                                if (time((time_t *)NULL)
                                    >= startime + LONGTIME) {
                                        longloopmessage();
                                        loopcount = -1;
                                }
                        }
                }
                lnloop = 0;
        }

        /*
         * We might as well cache it.
         */
        add_lnum(lno, cpos);
        return (lno);
}

/*
 * Return the line number of the "current" line.
 * The argument "where" tells which line is to be considered
 * the "current" line (e.g. TOP, BOTTOM, MIDDLE, etc).
 */
currline(where)
        int where;
{
        off_t pos, ch_length(), position();

        if ((pos = position(where)) == NULL_POSITION)
                pos = ch_length();
        return(find_linenum(pos));
}
